Age-related hearing loss is undoubtedly multifactorial, combining genetic predispositions with a plethora of lifetime insults to the auditory organ. Therefore, no single model may encompass all facets of presbycusis and research has to select appropriate approaches to selected aspects that may contribute to this pathology. The proposed project explores a major hypothesis of aging namely that reactive oxygen species (ROS) are major contributors to age-related tissue dysfunction. The evidence behind this hypothesis is compelling and preliminary data are highly suggestive that both endogenous antioxidant defenses and redox-sensitive signaling pathways decline in the aging cochlea leaving cochlear tissues and cells prone to oxidative injury and death. The hypothesis will be addressed at several levels in four specific aims. The first aim will assess cochlear pathology in aging CBA mice and measure the intrinsic antioxidants defense systems (glutathione, antioxidant enzymes) that maintain the cellular redox status. The second aim will determine the activity of redox-regulated signaling pathways that restore redox homeostasis. The control of these pathways requires the concerted efforts of second messengers, protein kinases, and transcription factors that will ultimately change the pattern of gene expression in the cell. Consequently, the third aim will analyze the expression of redox-related genes in aging CBA mice and compare this pattern to gene expression in progeny of four-way crosses (bred in Project 0003) with accelerated hearing loss. Finally, the fourth aim proposes to supplement nutritional antioxidants in an effort to restore redox homeostasis in aging animals and attenuate an oxidative stress-based cochlear failure. The results of this study, together with the results from projects 0002 and 0003, will allow us to formulate a hypothesis of stress-related injuries to the aging cochlea. Such knowledge and the potential attenuation of hearing loss by antioxidants may have far reaching consequences for the treatment of presbycusis.